The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Many motor vehicle transmissions, both dual clutch automatic (DCT) and manual types, depend upon splash lubrication to provide lubrication to their moving parts. Essentially splash lubrication comprehends submerging certain components at least partially in transmission fluid and relying upon the fluid drawn into the rotating components and thrown or slung about the transmission in mist or droplets to adequately lubricate all the transmission components.
This lubrication scheme therefore depends, to a great extent, on the submergence depth of the components and such depth, of course, depends simply upon how filled with fluid the transmission housing is. Clearly, therefore, splash lubrication, solely from a lubrication standpoint, is more effective the more or the higher the fluid level is in the transmission.
Simply substantially filling the transmission with fluid is not a reasonable approach, however, as excessive transmission fluid adds weight, increases losses in the transmission and is costly. Thus it is an appropriate engineering inquiry to determine how to provide the maximum necessary lubrication with minimum transmission fluid.
An approach long utilized is to attempt to closely conform the inside surface and volume of the transmission to the contours and outline of the gears, shafts and other components such that large regions or pockets of essentially inactive lubricant are eliminated. While this is generally done, the demands of metal casting techniques, that is, the need to have draft in the molds to facilitate removal of the castings from the mold limits the viability of this approach.
Another approach has been the installation of fillers in transmissions—complex inserts which conform on one or more sides to the internal contours of the transmission housing and on other sides to transmission components such as shafts or gears. Since they are fluid tight and fabricated of lightweight materials, such fillers both displace the transmission fluid, thereby requiring less volume to fill the transmission and lower the overall weight of the transmission.
Oftentimes such fillers are hollow, blow molded articles. Such blow molded fillers, when intact, provide excellent volume to weight ratios but are unfortunately prone to leakage and rupture. When such a blow molded filler fails, it fills with transmission fluid. Thus, the lubrication fluid level in the transmission lowers and effective splash lubrication action may be compromised.
Another filler construction utilizes two molded halves having friction welded flanges. Here, a pair of mating flanges extends around the parting line of the two halves of the filler and the filler is assembled by friction welding the two flanges together. While such a construction is generally stronger than a blow molded filler, the peripheral friction welded flange reduces the overall size and volume of the device and thus reduces its displacement and effectiveness.
While it is apparent from the foregoing that transmission fillers serve a practical and useful purpose in motor vehicle transmissions, it is also apparent that improvements in them are desirable.